1. Field of the Invention
The present invention relates to an inspecting system and an inspecting method both using an electron beam, both of which inspect a semiconductor device having micro-fabricated patterns, a substrate, a photomask (exposure mask), a liquid crystal, etc.
2. Description of the Related Art
In order to detect the occurrence of abnormalities and defects in a manufacturing process of a semiconductor device in early stages or in advance, the inspection of patterns on a semiconductor wafer is carried out upon completion of respective manufacturing process steps.
As a method of inspecting such defects, a method and a system for inspecting each of patterns through the use of an electron beam image high in resolution have been put into practical use.
There is a need to acquire or obtain a high SN image at a very high speed with a view toward performing high throughput and high-accurate inspections with an increase in bore diameter of a wafer and a scale-down of each circuit pattern. Therefore, the number of electrons applied through the use of a large current beam of 1000 times or more (of 10 nA or more) one for a normal scanning electron microscope (SEM) is ensured and a high SN ratio is maintained. It is also essential that secondary electrons generated from a substrate and reflected electrons are detected at high speed and with high efficiency. A low accelerating electron beam of 2 KeV or less is applied so that a semiconductor substrate with an insulating film such as a resist or the like is not placed under the influence of charging.
JP-A No. H10 (1998)-12170 discloses a technology wherein in a scan type charged particle beam device capable of varying a scanning speed, a digital circuit matches the timing for blanking-signal OFF with the timing provided to start the capturing of image data in order to prevent a distortion of an image caused by a distortion of a scan signal at an image take-in or capturing start time at the time that a scanning speed is fast.
JP-A No. 2000-100362 describes a system for digitally controlling various timings at a fast beam scan.
A SEM type inspecting system has the possibility that since a desired image acquisition area is irradiated with a beam by one pixel from its end to form an image signal, the neighborhoods of both ends in the area will differ from its central portion in conditions such as the amount of abeam current, thereby varying the quality of an image. From the necessity that the center of the beam is placed in the center of the area, large deflection distortions occur in both ends of the image acquisition area. This is not undesirable as an electron optical condition. When comparison checking is made using an image placed under such an adverse condition, the performance of inspection might be degraded.
Even if the prior art is applied to the inspection SEM, the degradation in inspection performance at both ends of the image acquisition area cannot be prevented from occurring.
A problem arises in that a screen condition related to a detection area placed under inspection cannot be confirmed through a monitor.
An object of the present invention is to provide an inspecting system or method using an electron beam, capable of confirming a screen condition related to a detection area placed under inspection by means of a monitored image.
Another object of the present invention is to provide an inspecting system or method using an electron beam, capable of preventing degradation in inspection performance due to a change in image quality and deflection distortions at ends of an inspected image, a shading phenomenon, etc.
According to one aspect of the present invention, when a defect in a sample is detected based on a detected signal of secondary charged particles, for example secondary electrons, generated by causing an electron beam to scan, such a defect is detected based on an image signal in which both ends of a scan area are deleted.
According to another aspect of the present invention, areas each having a predetermined width at its scan start end and scan completion end, and image areas lying therein are distinctively displayed on a monitor.
According to a further aspect of the present invention, blanking or a synchronizing signal for taking in or capturing an image is controlled to exclude both ends lying in a scan area from a defect inspection area.
According to one preferred embodiment of the present invention, electron beam scanning means executes a high-speed or fast scan on a sample in a first direction and a low-speed or slow scan on the sample in a second direction different from the first direction in the form of their compresence. Areas at both ends in a scan area, which are not used in image comparing means, are set by blanking as viewed in a fast scan direction, whereas they are set according to activation and inactivation of a synchronizing signal as viewed in a low-speed or slow scan direction.
Owing to these, an inspecting system using an electron beam can confirm high-accuracy timing matching in units of 10 ns on a monitored image. An inspecting system or method using an electron beam can be provided which prevents degradation in the accuracy of inspection with instability of a swing start and a swing end at both ends of a scan area as viewed in a high-speed direction or a low-speed direction and has higher-accuracy inspection performance.
Other objects and features of the present invention will be demonstrated by the description of the following embodiments.